The present disclosure relates to solid-state imaging devices, and more particularly, to charge coupled device (CCD) type solid-state imaging devices.
In recent years, with the rapid proliferation of digital cameras, digital video/still cameras, and camera-equipped mobile phones, demand for solid-state imaging devices has been rapidly growing. Recently, in particular, with the need for increase in the number of pixels and adaptation to moving pictures, solid-state imaging devices achieving a balance between finer pixel size and higher drive speed have been in high demand. As one solution answering this request, proposed is a low-resistance transfer electrode structure in which a transfer electrode is constructed of a multilayer film of a high-resistance electrode film made of polysilicon or the like and a low-resistance electrode film made of aluminum, tungsten, silicide, or the like (see Japanese Patent No. 3255116 (Document 1), for example).
A basic structure of a conventional solid-state imaging device will be described.
FIG. 9 is a view schematically showing the entire configuration of a conventional solid-state imaging device.
The conventional solid-state imaging device of FIG. 9 includes a plurality of pixels 2 arranged in a matrix (in rows and columns in the horizontal and vertical directions) with spacing from one another on a semiconductor substrate 1 made of an n-type silicon substrate. The region having the pixels 2 arranged in a matrix constitutes an image formation region 3.
The plurality of pixels 2 include a plurality of vertical transfer channels 4 extending in the vertical (column) direction and a plurality of photodiodes 5 arranged in a matrix with each column of photodiodes 5 being adjacent to each of the vertical transfer channels 4. A horizontal transfer channel 6 extending in the horizontal (row) direction is also formed on the semiconductor substrate 1 at the ends of the vertical transfer channels 4 in the transfer direction (vertical direction). An output amplifier 7 is provided at the output end of the horizontal transfer channel 6. The arrows a to c in FIG. 9 indicate the charge transfer directions.
In a region surrounding the image formation region 3, a plurality of vertical bus lines 8 run along the periphery of the image formation region 3, and different transfer pulses φV1 to φV4 are supplied to the different vertical bus lines 8 from outside. Also, a plurality of horizontal bus lines 9 run along the horizontal transfer channel 6, and different transfer pulses φH1 and φH2 are supplied to the different horizontal bus lines 9 from outside.
A plurality of vertical transfer electrodes 10 extend in the horizontal direction above the vertical transfer channels 4, and are connected to any of the vertical bus lines 8 at their both ends. Likewise, a plurality of horizontal transfer electrodes 11 are formed above the horizontal transfer channels 6, and are connected to any of the horizontal bus lines 9 at their ends.
The configuration of each pixel of the solid-state imaging device of FIG. 9 will be described in a concrete manner.
FIG. 10 is a cross-sectional view of a pixel shown in FIG. 9 in the vertical direction.
As shown in FIG. 10, a plurality of vertical transfer channels 22 extending in the column direction and a plurality of photodiodes (PD) 23 arranged in a matrix with spacing from one another are formed in a surface portion of a semiconductor substrate 21. A gate insulating film 24 is formed on the entire surface of the semiconductor substrate 21 to cover the vertical transfer channels 22 and the photodiodes 23. A plurality of vertical transfer electrodes 27, each constructed of a gate electrode 25 and a metal light-shielding film 26, are formed on the gate insulating film 24 so as to expose part of each of the photodiodes 23 while covering the vertical transfer channels 22. An interlayer insulating film 28 is formed on the gate insulating film 24 to cover the vertical transfer electrodes 27 and have recesses formed above the photodiodes 23, and a high refractive-index film 29 is formed on the interlayer insulating film 28. The interlayer insulating film 28 and the high refractive-index film 29 constitute inner lenses 30. A flattening film 31 is formed on the high refractive-index film 29, and color filters 32 are formed on the flattening film 31. Another flattening film 33 is formed on the color filters 32, and top lenses 34 are formed on the flattening film 33. In the pixel structure configured as described above, light L condensed by each top lens 34 is incident on the opening above each photodiode 23 via the corresponding inter lens 30.
Next, the pixel structure of a solid-state imaging device of the first prior art example described in Document 1 above will be described.
FIGS. 11A-11E are a plan view (FIG. 11A), horizontal cross-sectional views (FIGS. 11D and 11E), and vertical cross-sectional views (FIGS. 11B and 11C) showing the pixel structure of the solid-state imaging device of the first prior art example, where the cross-sectional views of FIGS. 11B-11E are respectively taken along line XIb-XIb, line XIc-XIc, line XId-XId, and line XIe-XIe in the plan view of FIG. 11A. Note that illustration of the components shown in the cross-sectional views is partly omitted in the plan view of FIG. 11A for the sake of convenience.
As shown in FIGS. 11A-11E, in the pixel structure of the solid-state imaging device of the first prior art example, a plurality of vertical transfer channels 42 extending vertically and a plurality of photodiodes (PD) 43 arranged in a matrix are formed in a surface portion of a semiconductor substrate 41. A gate insulating film 44 is formed on the entire surface of the semiconductor substrate 41 to cover the vertical transfer channels 42 and the photodiodes 43. On the gate insulating film 44, a plurality of first and second vertical transfer electrodes 47a and 47b, each of which is constructed of a gate electrode 45 and a metal light-shielding film 46 made of tungsten, aluminum, silicide, salicide, or the like, are formed alternately in the vertical direction in such a manner as to expose part of each of the photodiodes 43 while covering the vertical transfer channels 42. A light-shielding resin 48 is formed in the gaps between the first vertical transfer electrodes 47a and the second vertical transfer electrodes 47b and on the sidewalls of the first and second vertical transfer electrodes 47a and 47b exposed in openings 43R (see FIG. 11A) formed to expose the photodiodes 43.
An interlayer insulating film 49 is formed on the gate insulating film 44 to cover the first and second vertical transfer electrodes 47a and 47b and have recesses formed above the photodiodes 43, and a high refractive-index film 50 having a refractive index higher than the interlayer insulating film 49 is formed on the interlayer insulating film 49. The interlayer insulating film 49 and the high refractive-index film 50 constitute inner lenses 51. Although not shown, a flattening film, color filters, another flattening film, and top lenses are formed in this order on the high refractive-index film 50 as those shown in FIG. 10.
The pixel structure of a solid-state imaging device of the second prior art example described in Document 1 will then be described.
FIGS. 12A-12C are a plan view (FIG. 12A) and horizontal cross-sectional views (FIGS. 12B and 12C) showing the pixel structure of the solid-state imaging device of the second prior art example, where the cross-sectional views of FIGS. 12B and 12C are respectively taken along line XIIb-XIIb and line XIIc-XIIc in the plan view of FIG. 12A. Note that illustration of the components shown in the cross-sectional views is partly omitted in the plan view of FIG. 12A for the sake of convenience. Note also that the vertical cross-sectional views of FIGS. 11B and 11C also apply to the solid-state imaging device of the second prior art example.
The solid-state imaging device of the second prior art example shown in FIGS. 12A-12C is the same in pixel structure as the solid-state imaging device of the first prior art example except for the regions where the light-shielding resin 48 is formed. More specifically, the light-shielding resin 48 in the solid-state imaging device of the second prior art example is not formed on the sidewalls of the first and second vertical transfer electrodes 47a and 47b exposed in the openings 43R (see FIGS. 12A and 12B). Moreover, the regions of the light-shielding resin 48 formed in the gaps between the first and second vertical transfer electrodes 47a and 47b recede inward at portions exposed in the openings 43R (see FIGS. 12A and 12C).